The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
I.E.E.E. sections 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(h), and 802.11(n) (collectively sections 802.11), which are incorporated herein by reference in their entirety, define ways for configuring wireless networks and devices. According to these standards, wireless network devices may operate in either an ad-hoc mode or an infrastructure mode.
Referring now to FIGS. 1 and 2, in the ad-hoc mode, each client station 10-1, 10-2, . . . , and 10-N (collectively client stations 10) communicates directly with other client stations 10 without requiring an access point (AP). In FIG. 2, in the infrastructure mode, each client station 20-1, 20-2, . . . , and 20-M (collectively client stations 20) communicates with other client stations 20 through an AP 24. The AP 24 may provide a connection to a network 26, a server 28, and/or for the Internet 30.
Referring generally to FIGS. 3A-3B, a wireless network device (hereinafter device) 50 is shown. The device 50 may be the AP 24 or one of the client stations 10, 20. In FIG. 3A, the device 50 may comprise at least one antenna 52, a physical layer (PHY) module 54, and a medium access controller (MAC) module 56. Additionally, the device 50 may include a processor 58 and other components. The PHY module 54 may communicate with the medium (i.e., air) via the antenna 52. The PHY module 54 may comprise a radio frequency (RF) transceiver module 55 that transmits and receives data to and from the medium via the antenna 52. The MAC module 56 may communicate with the PHY module 54 and the processor 58.
In FIG. 3B, the RF transceiver module 55 may comprise a transmitter module 70 that transmits data and a receiver module 72 that receives data in the form of modulated RF carriers via the antenna 52. The transmitter module 70 may comprise an encoder module, a modulator module, an analog-to-digital converter (ADC) module, etc. (all not shown). The receiver module 72 may comprise an automatic gain control (AGC) module, a filter module, an ADC converter module, a demodulator module, a decoder module, etc. (all not shown).
802.11 provides that data may be simultaneously transmitted via multiple channels in a predetermined frequency-band. For example, devices that comply with section 802.11(a) may transmit data at 20 MHz via eight 20 MHz channels in a 5 GHz frequency-band; devices that comply with section 802.11(b) may transmit data at 20 MHz via fourteen 20 MHz channels in a 2.4 GHz frequency-band, etc.
Devices that comply with section 802.11(n) may transmit data at 20 MHz or 40 MHz via a 40 MHz channel. The 40 MHz channel may comprise two 20 MHz channels. A first 20 MHz channel is called a primary channel or a control channel. A second 20 MHz channel is called a secondary channel or an extension channel. The 802.11(n)-compliant devices may transmit data at 40 MHz via the 40 MHz channel when communicating with other 802.11(n)-compliant devices. Additionally, 802.11(n)-compliant devices may transmit data at 20 MHz via the control channel when communicating with the devices that comply with 802.11 sections other than 802.11(n).
A wireless network (hereinafter network) may include devices that comply with different 802.11 sections. For example, the network may comprise the AP 24 and a first set of client stations 20 that complies with section 802.11(n). Additionally, the network may include a second set of client stations 20 that comply with 802.11 sections other than section 802.11(n) (e.g., 802.11(a), 802.11(b), 802.11(g), etc.). The AP 24 may transmit and receive data at 40 MHz via the 40 MHz channel when communicating with the first set of client stations 20 and may transmit and receive data via the 20 MHz control channel when communicating with the second set of client stations 20.
Occasionally, the AP 24 may transmit data at 40 MHz when data transmitted by devices in other networks may be present in the extension channel. For example, other networks may include devices that comply with 802.11 sections other than section 802.11(n) and that transmit data at 20 MHz in a channel that may overlap with the 20 MHz extension channel of the AP 24. Consequently, collisions may occur when the AP 24 transmits data at 40 MHz.
Additionally, collisions may occur when the AP 24 transmits data at 40 MHz while other devices that comply with 802.11 sections other than section 802.11(n) communicate in the network at 20 MHz via the extension channel. Collisions may also occur when multiple devices that comply with the section 802.11(n) simultaneously transmit data in the network.
When collisions occur, data may get corrupted. Corrupted data may be discarded when received. When data received is corrupted, the data may have to be retransmitted. Thus, collisions may decrease throughput and quality of service (QoS) of the network.
To minimize collisions, devices in wireless networks utilize a carrier sense multiple access (CSMA) protocol to determine when a channel is free to transmit data. Ideally, only one device may transmit data via the channel at a given time. Typically, the devices “listen” for activity (i.e., the devices sense presence or absence of RF carriers) in the channel before transmitting data via that channel. Listening for activity is generally referred to as carrier sensing (CS). Since multiple devices perform CS by simultaneously accessing the medium (i.e., air), the protocol is called carrier sense multiple access protocol. Activity in the channel may also be sensed by performing energy detection (ED), wherein presence or absence of RF energy in the channel is detected.
Specifically, the PHY module 54 may generate clear channel assessments (CCAs) for the control and extension channels based on whether radio frequency (RF) activity is present or absent in the channel. The CCAs may indicate whether the channels are busy or free. Typically, the CCA for the channel is asserted (i.e., when CCA=1) when a channel is busy, and the CCA for the channel is cleared when the channel is free (i.e., when CCA=0). The terms clear, free, and idle are used interchangeably and synonymously throughout this disclosure.
The PHY module 54 may communicate the CCAs to the MAC module 56. Based on the CCAs, the MAC module 56 may decide whether to transmit data via the channel. For example, the MAC module 56 may decide that data may be transmitted via a channel when the channel is free (i.e., when CCA=0). Additionally, the MAC module 56 may decide to “back off” (i.e., to not transmit data) when the channel is busy (i.e., when CCA=1).